JPH09150348A - Cutting error correcting method in nc machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide sufficient dimension precisional in a short required machining time by adding an excessive cutting equivalent to a deflection quantity stored in compliance with a tool position and securing dimension precision for a machined workpiece when the same workpiece is machined. SOLUTION: For each position of a cutting tool 1 on a tool path, a plurality of measuring points are selected in a workpiece 3, including the workpiece 3 whose cross section is altered. In each of positions Z0-Z8 on the workpiece 3, a deflection quantity α is measured, and a deflection quantity α in an unmeasured point is estimated on the basis of linear interpolation, and then, a solid line of the deflection quantity α is provided. Subsequently, cutting error correction is carried out, so that all the shortages in cutting due to a deflection of the workpiece 3 can be filled up when the cutting tool 1 is shifted along a movement locus which is formed by adding an excessive cutting correction quantity α in each position to the X-axis coordinate for an outline of a product contour in the present position of the cutting tool 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting error correction method for an NC machine tool.

[0002]

2. Description of the Related Art When a thin workpiece is machined by an NC machine tool, particularly a lathe machine, the workpiece is bent due to a pressing force due to the cutting of the tool.
In some cases, the required depth of cut is insufficient and machining accuracy may deteriorate.

Such a problem is solved by a conventional balance cutting function, that is, a function in which a tool rest for lathe processing is provided on both sides of a work and symmetrical processing is performed from both sides of the center axis of the work. However, since a control function for two systems is required, usable machines and control devices are significantly limited. Needless to say, this balance cut function cannot be applied to anything other than lathe processing capable of cutting a workpiece from both sides.

In lathe machining using a normal machine and control device, the amount of cutting is restricted so that the bending of the work does not exceed an allowable range, and the bending of the work is prevented. However, as a result, heavy cutting becomes difficult, and there is a problem that the processing time as a whole becomes long.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to perform processing symmetrical with respect to the center axis of the work and to limit the depth of cut.
An object of the present invention is to provide a cutting error correction method for an NC machine tool that can obtain sufficient dimensional accuracy in a short machining time.

[0006]

According to the present invention, a pressing force acting in a cutting direction of a tool when a work is cut with a set cutting depth is obtained, and the pressing force presses the work at each tool position on a machining path. The amount of flexure of the work that occurs when the above is measured and stored in advance corresponding to each tool position on the machining path, and when machining the same work, excess cutting corresponding to the stored amount of flexure according to the tool position The above-mentioned object was achieved by a configuration characterized by ensuring the dimensional accuracy of the machined work by adding

Further, since it is actually difficult to measure the deflection amount of the work at all tool positions on the machining path,
On the machining path at each position between each measurement point, calculate the amount of work deflection caused by the pressing force of the tool using multiple tool positions on the machining path as measurement points and interpolate the data of the work deflection amount at each measurement point. The amount of bending of the workpiece was estimated.

The tool position selected as the measurement point is
At least, it is desirable to select a position where a large change occurs in the bending tendency of the work, that is, a tool position on the machining path where the cross-sectional area of the work changes discontinuously.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing a main part of a control device 100 for driving and controlling an NC machine tool,
Further, FIG. 2 is a conceptual diagram showing a main part of an NC lathe as a machine tool. In FIG. 2, reference numeral 1 is a bite (cutting tool) attached to a tool rest of an NC lathe, reference numeral 2 is a chuck for eating a rod or the like which is a material of the work 3, reference numeral 4 is shown.
Is a tailstock shaft that projects into a center hole formed in one end surface of the work 3 and rotatably supports the work 3.

The chuck 2 is driven to rotate about a Z axis in FIG. 2 by a spindle motor 62 described later, and the tool rest on which the cutting tool 1 is mounted is a servo motor 50 for each of X and Z axes described below.
By means of 51, translation is made in the directions of the X and Z axes according to the machining program.

As shown in FIG. 1, the processor 11 of the control device 100 is a processor which controls the control device 100 as a whole. The processor 11 reads the system program stored in the ROM 12 via the bus 21, and according to the system program, the control device 10
0 is totally controlled. The RAM 13 stores temporary calculation data, display data, various data input by the operator via the CRT / MDI unit 70, and the like. The CMOS memory 14 is configured as a non-volatile memory that is backed up by a battery (not shown) and retains its storage state even when the power supply of the control device 100 is turned off. The machining program and the CRT / MDI unit read via the interface 15 are provided. A machining program or the like input via 70 is stored. Also, R
The OM 12 is pre-written with various system programs for carrying out edit mode processing and automatic operation processing required for creating and editing a machining program.

The interface 15 is the control device 100.
Is an interface for an external device that can be connected to the external device 72, and is connected to an external device 72 such as a floppy cassette adapter. A processing program or the like is read from the external device 72, and the processing program edited in the control device 100 can be stored in a floppy cassette or the like via the external device 72.

A PMC (Programmable Machine Controller) 16 controls an auxiliary device on the NC lathe side, for example, an actuator such as a robot hand for tool change, by a sequence program built in the control device 100. That is, according to the M function, S function, and T function instructed by the machining program, these sequence programs convert the signals into those required by the auxiliary device, and the I / O unit 1
Output from 7 to the auxiliary device side. Auxiliary devices such as various actuators are operated by this output signal. Also, it receives signals from various switches of the operation panel provided on the main body of the NC lathe, performs necessary processing, and passes the signals to the processor 11.

Image signals such as the current position of each axis of the NC lathe, alarms, parameters and image data are sent to the CRT / MDI unit 70 and displayed on its display.
The CRT / MDI unit 70 is a manual data input device having a display, a keyboard, and the like. The interface 18 receives data from the keyboard of the CRT / MDI unit 70 and passes the data to the processor 11. The interface 19 is connected to the manual pulse generator 71 and receives pulses from the manual pulse generator 71. The manual pulse generator 71 is mounted on the operation panel of the NC lathe, and is used for precisely positioning the tool post of the NC lathe by controlling each axis by the distribution pulse based on the manual operation.

The axis control circuits 30 to 31 for the X and Z axes for moving the tool rest of the NC lathe receive the movement commands for the axes from the processor 11 and output the commands for the axes to the servo amplifiers 40 to 4.
Output to 1. In response to this command, the servo amplifiers 40 to 41 drive the servo motors 50 to 51 of each axis of the NC lathe. The servomotors 50 to 51 for the respective axes have a built-in position / speed detector, and a position / speed feedback signal is fed back from this position / speed detector.
Although the description of the feedback of the position signal and the feedback of the velocity is omitted in FIG. 1, each of the basic position, velocity, and current loops is excluded except for the process of adding the correction value related to the correction of the cut amount of the X axis. The process is similar to that of conventional controllers and NC lathes (see Figure 5).

The spindle control circuit 60 receives a spindle rotation command to the NC lathe and outputs a spindle speed signal to the spindle amplifier 61. The spindle amplifier 61 receives the spindle speed signal, rotates the spindle motor 62 of the NC lathe at the commanded rotation speed, and rotationally drives the work 3 bitten by the chuck 2. A position coder 63 is coupled to the spindle motor 62 by a gear or a belt,
The position coder 63 outputs a feedback pulse in synchronization with the rotation of the main shaft, and the feedback pulse is output by the interface 20.
Read by the processor 11 via.

Next, the principle of operation of this embodiment will be described by taking as an example the case where the cutting error is corrected in the final finishing of the work 3.

As already mentioned in the section of operation, the present invention is
Since the cutting tool 1 serving as a cutting tool eliminates the insufficient cutting caused by the bending of the work 3 caused by pressing the work 3, in order to carry out this,
First of all, it is necessary to obtain data on the amount of bending that occurs in the work 3 in the cutting state.

The term "deflection" as used herein refers to a cutting amount set by normal position control based on a machining program, and is a cutting tool 1
Because the pressing force that acts on the cutting tool 1 when cutting the work 3 with the set depth of cut is not the bending that occurs in the work 3 when the work 3 is rushed into the surface of the work 3 for cutting. Is the bending that occurs in the work 3, and there are the following differences between them.

That is, with the set depth of cut, for example, as shown in FIG.
Insert the bite 1 into the surface of the work 3 at the position P0 of
After that, even if the cutting tool 1 is moved along the machining path of the contours P0 to P8 of the final finished shape, in reality, P0 to P8 (the Z axis position is z0 to z8) due to the pressing force of the cutting tool 1 during cutting. At each tool position, the deflection α'as shown by the alternate long and short dash line in FIG. 3 occurs. This α'is the above-mentioned "deflection that occurs in the work 3 when the cutting operation is performed by causing the cutting tool 1 to penetrate into the surface of the work 3 with the cutting amount set by the normal position control based on the processing program".
It is.

As a result of this bending, the work 3 escapes from the tip of the cutting tool 1 to cause insufficient cutting corresponding to α'at each position of the work 3, but the normal position control based on the machining program is performed. In addition to α ′ at each position of byte 1
Even if the cutting process is performed by inserting an excessive cut corresponding to, the dimensions of the finished shape formed thereby do not match the finished dimensions as shown by the contours P0 to P8.

At the central portion of the work 3, for example, at the position of z5 corresponding to the center of the support beams at both ends, since the work 3 is in a state of being easily bent, it corresponds to α'in addition to the normal position control based on the machining program. Work piece 3 with excess cut
This is because, even if is pressed, the work 3 further bends beyond α'when the cut is actually made, so that the work 3 does not have a cut corresponding to the set cut amount.

In order to eliminate such insufficient cutting,
It is necessary to press the work 3 with a force corresponding to "a pressing force acting in the cutting direction of the cutting tool 1 when the work 3 is actually cut with the set depth of cut" to perform the cutting process. Of course, the contouring of the final finish by the NC lathe is not to perform the cutting by the copying control based on the surface of the workpiece 3 processed in the cutting process immediately before that, but to obtain the final product shape. It should be performed according to the position control based on the program, and the control of the cutting is not performed by the control of the driving torque, that is, the pressing force of the cutting tool 1, but should be performed by the position control until it gets tired. A correction value for eliminating the shortage must also be given as a position command value.

Theoretically, the tool 1 is moved in the Z-axis direction while always applying "the pressing force acting in the cutting direction of the cutting tool 1 when the work 3 is actually cut with the set cutting amount" to the cutting tool 1. If the cutting process is performed, the depth of cut should be always given from the surface of the work 3,
The shape and dimensions that should be obtained by the final finishing must be in line with the design data, that is, the contour shape of the machining program as shown by P0 to P8, and must be obtained in the roughing and semi-finishing steps. It should not be constrained according to the shape of the workpiece 3 thus obtained.

In other words, the amount of excess cutting to be given to the cutting tool 1 at each position of the machining path is correct, "due to the pressing force acting in the cutting direction of the tool 1 when the work 3 is actually cut with the set cutting amount. The amount of bending that occurs in the work 3 ", and all the processing errors caused by the bending of the work 3 are eliminated only by the correction operation due to this excessive cutting.

Naturally, the value of "the amount of bending generated in the work 3 due to the pressing force acting in the cutting direction of the cutting tool 1 when the work 3 is actually cut with the set depth of cut" is held in the shape of both ends supporting beam. Further, each position on the work 3, that is, each position of the cutting tool 1 on the tool path is different, and is affected by the change in the cross-sectional shape (thickness) of the work 3.

Therefore, in this embodiment, first,
Using the work 3 or another test piece having the same material as the work 3, "the pressing force F acting in the cutting direction of the cutting tool 1 when the work 3 is actually cut with the set cutting amount" is obtained. That is, the work 3 or another test piece having the same material as that of the work 3 is attached to the chuck 2 and the tailstock shaft 4 in the state shown in FIG. 2, and the work 3 or the test piece is attached to the test piece while rotating the spindle. At a position where bending is least likely to occur, for example, at a position of z0, the X-axis servomotor 50 is driven by position control to cause the cutting tool 1 to be inserted into the work 3 or the test piece by a set cut amount.
At this time, the reaction force F acting on the cutting tool 1 is measured as the drive current of the X-axis servomotor 50.

That is, the measured value of F is obtained by holding the work 3 or the test piece in a non-deflected state.
Or, it is the pressing force acting in the cutting direction of the cutting tool 1 when a cut amount of the set cut amount is made in the test piece,
This pressing force is the above-mentioned "pressing force F acting in the cutting direction of the cutting tool 1 when the work 3 is actually cut with the set cutting amount".

Therefore, next, a work 3 finally finished to the size of the product is prepared, the tool 1 is moved to each position of z0 to z8, and the driving torque of the X-axis servo motor 50 is pressed. In the state of being limited to F, the manual pulse generator 71 is operated at each position to move the bite 1 in the −x direction, and the amount α of deflection caused by the pressing force F is z0 to z.
Measure at each position of 8.

For example, a counter for counting the position feedback pulses from the X-axis servomotor 50 is provided, and the value is displayed so that the tool 1 is completely retracted from the work 3 and the manual pulse generator is provided. 71, the constant-speed rotation of the handle 71 is started to move the bite 1 in the -x direction, and the stepping pace of the counter for counting the position feedback pulse starts to slow down, that is, the tip of the bite 1 is the surface of the work 3. The value of the counter at the time of hitting is recorded, and further, the rotation of the handle of the manual pulse generator 71 is continued, and even when this is done, the counter value is not stepped at all, that is, the byte 1 is pushed. If the value of the counter at the time when the work 3 is fully bent by the pressure F is read and the difference between the two is obtained, the amount α of bending that occurs in the work 3 due to the pressing force F can be measured. That.

If a more precise measurement is required, the work 1 should be completely retracted from the work 3 and the work 3
Place a dial gauge underneath and attach the probe tip to the work 3.
The reading at that time is recorded near the center of the lower surface of the No. 3, and the value of the dial gauge is read while the work 3 is fully bent by the same operation as described above. It suffices to measure the amount α.

Since it is not possible to uniformly measure the deflection amount α at all the positions of the cutting tool 1 on the tool path, a plurality of measurement points including the position where the cross-sectional shape of the work 3 changes are selected. The deflection amount α at the position is measured, and the deflection amount α is estimated from the measurement value immediately before and after the non-measurement portion. An example in which the bending amount α is measured at each position of z0 to z8 on the work 3 and the bending amount α of the non-measured portion is estimated by linear interpolation is shown in FIG.

Further, in this embodiment, the CMOS memory 14 is provided with a data file as shown in FIG. 4, and zi-1 to zi of i = 1 to j on the machining path in the work 3 are provided.
Slope ai of the interpolation line and the bending axis intercept bi in each section of
In the cutting error correction process described later,
Depending on which section the current position of the cutting tool 1 in the axial direction belongs to, the correction value α of the excessive cutting depth is determined by the expression α = ai × [position of the cutting tool 1 in the z-axis direction] + bi. The values of the slope ai of the interpolation straight line and the deflection axis intercept bi in each section can be easily obtained by the equation of the straight line passing through two points, and of course, [the measurement result of the z-axis component of the measurement position and the deflection α at that position] By inputting as many sets as the number of measurement points, it is possible to automatically create a data file by obtaining the values of ai and bi in the internal processing of the control device 100.

FIG. 6 shows the processor 11 at the final finishing stage based on the data file created in this way.
5 is a flowchart showing an outline of a cutting error correction process executed by the above process, and this process is repeatedly executed every position loop processing cycle of the processor 11. The work 3 to be cut by the final finishing process is, of course, the work 3 after the roughing or the semi-finishing process and before the final finishing process, and is not the work 3 that has been processed into the above-described product shape.

Processor 1 which started the cutting error correction processing
First, based on the speed command and the movement command of the machining program for moving the cutting tool 1, the same pulse distribution processing as in the conventional case is executed to obtain the pulse distribution amounts Δx and Δ in the X and Z axis directions.
z (see FIG. 5) is calculated (step S1), the distribution amount Δz in the z-axis direction is added to the current value storage register A (z) that stores the z-axis current position, and the byte 1 is moved by this movement command. Store the z-axis coordinate of the destination (step S
2). The Z-axis coordinate z0 of the start position of the final finishing process
Is automatically stored in the correction execution position storage register B (z) at the start of execution of the final finishing process, and the value of the correction amount integration register A (α) is automatically initialized to zero at this stage. Shall be done.

Next, the processor 11 determines the correction execution position storage register B from the value of the current value storage register A (z).
The distance from the Z-axis position when the cutting amount is corrected in the previous processing by subtracting the value of (z) to the moving destination of the bite 1 by the distribution pulse output in the processing cycle | A (z) -B
(Z) | is determined, and it is determined whether or not this movement distance has reached the correction execution pitch P (set value) (step S).
3).

That is, in this embodiment, the excessive depth of cut is corrected only when the movement of the cutting tool 1 in the Z-axis direction reaches a certain amount and the change in the deflection of the work 3 becomes a problem. And this amount of movement | A (z)
Until −B (z) | reaches the correction execution pitch P,
Similarly to the conventional case, the distributed pulses Δx and Δz obtained in the process of step S1 are output as they are (step S13),
Axis control circuit 30, 31 for each axis and servo amplifier 40,
The servo motors 50 and 51 for the X and Z axes are controlled by 41 (see FIG. 5) to perform an interpolation operation for moving the cutting tool 1 (turret).

However, since the movement command of the distribution pulses Δx and Δz is an incremental amount, except for the section from the start position z0 of the final finishing process to z0 + P (the section until the first excessive cutting correction), The movement locus of 1 does not always coincide with the machining path according to the machining program. When the correction of the excessive cutting is already performed several times, naturally, the movement locus of the bite 1 is
The movement locus determined by the machining program is offset in the bending direction (−x direction).
Needless to say, the correction execution pitch P is far smaller in order than the distance between measurement points, for example, the distance between z0 and z1.

While the processes of steps S1 to S3 and step S13 are repeatedly executed, the movement destination A of the next byte 1 from the position B (z) where the previous correction operation was performed is performed.
When the Z-axis movement amount up to (z) reaches the correction execution pitch P and the determination result of step S3 becomes true, the processor 11
After initializing the section search index i (step S
4), the value is incremented by 1 to match the value i (= 1) indicating the first section (step S5), and the X-axis coordinates corresponding to the start point and end point of the section i from the data file as shown in FIG. read zi-1 and zi, byte 1
It is determined whether or not the destination A (z) of is within the section i (step S6).

If the destination A (z) of the byte 1 is not included in the section i, the processor 11 waits until the section i including the destination A (z) of the byte 1 is detected. Similar to the above, steps S5 and S6
The above process is repeatedly executed to obtain the section i including the destination A (z) of the byte 1.

Next, the processor 11 reads the inclination ai of the interpolation line and the bending axis intercept bi stored corresponding to the section i based on the value of the section search index i from the data file as shown in FIG. Step S7), based on these values and the value of the destination A (z) of byte 1, α = ai × A
According to the formula (z) + bi, the deflection α corresponding to the position of the moving destination A (z) of the cutting tool 1, that is, the correction amount α of the excessive cutting depth
Is obtained (step S8).

This value α is as shown in FIG.
It is the absolute amount when the state where the work 3 is not bent is set to zero, while Δx of the movement command is given as the incremental amount for each processing cycle of the position loop. It is necessary to recalculate the correction amount Δα for obtaining the absolute correction amount α (in short, the offset amount for the machining program) as the incremental amount at the destination A (z).

Therefore, the processor 11 subtracts the value of the correction amount integration register A (α) from the value of the deflection α corresponding to the position of the moving destination A (z) of the bite 1, and newly outputs the correction at this stage. The amount Δα, that is, if a movement command is output by Δα after that, the total correction amount matches the deflection α.
Is calculated (step S9, block 10 in FIG. 5).
0 processing), Δα is added to the distribution amount Δx in the X-axis direction obtained in the processing of step S1, and the result is stored again as the X-axis movement command Δx (step S10). As a result, if the tool rest of the cutting tool 1 is driven by the X-axis movement command Δx and the distribution amount Δz in the Z-axis direction obtained in step S1, the cutting tool 1 is set to the X-axis coordinate of the contour of the product shape at each position. Since it moves along the movement locus formed by adding the correction amount α for each position, all the insufficient cutting due to the bending of the work 3 is eliminated.

The processor 11, which has determined the X-axis movement command Δx required to correct the insufficient cutting, further adds the value of Δα calculated this time to the correction amount integration register A (α) to obtain the total correction amount. Update (step S11), move destination A (z)
Is stored in the correction execution position storage register B (z) as the correction execution position (step S12).

Then, the processor 11 outputs the distributed pulses Δx and Δz (step S13) as in the case where the correction process is not performed, and the axis control circuits 30 and 31 of each axis and the servo amplifiers 40 and 41 perform X. , Z-axis servo motors 50 and 51 are controlled (see FIG. 5) to perform an interpolation operation for moving the cutting tool 1.

Thereafter, the processor 11 repeatedly executes the same processing operation as described above for each processing cycle of the position loop, and as a result, each time the bit 1 moves by the correction execution pitch P in the Z-axis direction, the bit 1 of the bit 1 is changed. Until the cutting depth is corrected by Δα and the cutting tool 1 moves again in the Z-axis direction by the correction execution pitch P, the cutting tool 1 shifts the machining path determined by the machining program by α in the bending direction of the workpiece 3. Will move along.

Therefore, the change in the deflection α is neglected within the section of the correction execution pitch P, but as described above, the correction execution pitch P is much smaller than the order of the distance between the measurement points. Since it is set on the order, there is no substantial problem when the change in the deflection α is ignored in this section.

As described above, as one embodiment, the inclination ai of the interpolation straight line and the bending axis intercept bi are stored in the data file, and the correction amount α corresponding to the moving position of the cutting tool 1 is calculated, and this correction amount α is set. Integrated value A (α) of the correction amount up to that point
Although the correction value .DELTA..alpha. To be output as the incremental amount is obtained from the difference between (step S8, step S9), the sections zi-1 to z on the machining path are described.
The incremental correction value Δαi corresponding to the correction execution pitch P is obtained in advance for each i and stored in the data file (see FIG. 4), and the depth of cut is corrected with reference to this data file. It is also possible to do so. In short, the correction value Δαi is a value indicating the amount of change in the deflection for each section with the correction execution pitch P as a unit.

When the cutting correction is performed using the data file storing the correction value Δαi, instead of the processing of steps S7 to S11 in FIG. 6, the reading processing of Δαi (steps S7 to S9 and step S11 is performed). The alternative process) and the process of Δx ← Δx + Δαi (the alternative process of step S10) may be performed.

However, in this case, there is no guarantee that the time required for the bit 1 to move the correction execution pitch P is an integral multiple of the processing cycle of the position loop control, and the byte 1 has the correction execution pitch P. There is a case where the correction value Δαi is output after a delay after the movement, and it is unavoidable that the correction value Δαi is inferior to the above-described embodiment in terms of accuracy.

Of course, in the above-described embodiment as well, there is no guarantee that the time required for the byte 1 to move the correction execution pitch P will be an integral multiple of the processing cycle of the position loop control. Then, the correction amount α corresponding to the movement position of the cutting tool 1 is obtained, and the value obtained by subtracting the integrated value A (α) of the correction amounts up to that time from the correction amount α is the correction value Δα.
Therefore, the correction error due to the disagreement between the movement required time and the processing cycle is eliminated by the correction value Δα itself, and there is no problem that the correction error is accumulated.

In the above embodiments, the case where the present invention is applied to lathe processing has been described, but the present invention is
Unlike the conventional balance cut function, it does not eliminate the processing error by restricting the bending of the work due to the cutting force, but it bends the work in a natural state by the cutting force, and the excessive cutting corresponding to this bending Since processing error is eliminated by adding, in addition to lathe processing,
It can also be applied to processing with a milling machine or a grinding machine, that is, processing in which the work is cut from only one side (in the processing with a milling machine or a grinding machine, to improve the ground contact with the table and the dimensional accuracy. In some cases, the work may be bent while the work is fixed on the table with the feet left on the bottom of the work, or the box-shaped work is turned over to perform the work, so the work may bend. There are times when it is necessary to eliminate this).

[0053]

According to the cutting error correction method of the present invention, even if a deep cut is made in the work at the finishing stage, a working error due to the bending of the work does not occur, so that a short working time and sufficient dimensional accuracy can be obtained. Both can be realized.

Further, the use thereof is not limited to the lathe as in the conventional balance cut function, and the work due to the bending of the work is performed even for the work such as the milling process and the search process for cutting the work from only one side. The error can be eliminated.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a main part of a control device that drives and controls an NC machine tool.

FIG. 2 is a conceptual diagram showing a main part of an NC lathe as a machine tool.

FIG. 3 is a conceptual diagram showing a relationship between a Z-axis position on a machining path and a bending amount.

FIG. 4 is a conceptual diagram showing an example of a data file in which a bending amount of a work that occurs when a work is pressed is stored in association with a tool position on a machining path.

FIG. 5 is a functional block diagram showing an outline of position control in one embodiment.

FIG. 6 is a flowchart showing an outline of cutting error correction processing in the same embodiment.

[Explanation of symbols]

 1 byte (cutting tool) 2 chuck 3 work 4 tailstock shaft 11 processor 12 ROM 13 RAM 14 CMOS memory 15 interface 16 programmable machine controller 17 I / O unit 18, 19, 20 interface 21 bus 30, 31 axis control Circuit 40,41 Servo amplifier 50,51 Servo motor 60 Spindle control circuit 61 Spindle amplifier 62 Spindle motor 70 CRT / MDI unit 71 Manual pulse generator 72 Floppy cassette adapter 100 Controller

Claims (3)

[Claims] 1. A bending amount of a work that is generated when a pressing force acting in a cutting direction of a tool when a work is cut with a set cutting amount is obtained, and the pressing force presses the work at each tool position on a machining path. Is measured and stored in advance corresponding to each tool position on the machining path, and when machining the same work, by adding an excessive cut corresponding to the stored flexure amount according to the tool position A method for correcting a cutting error in an NC machine tool characterized by ensuring dimensional accuracy. 2. A plurality of tool positions on a machining path are used as measurement points to obtain a deflection amount of a work caused by a pressing force of the tool, and data of the deflection amount of the work at each measurement point is interpolated to obtain a distance between each measurement point. The method for correcting a cutting error in an NC machine tool according to claim 1, wherein the amount of bending of the work on the machining path at the position is estimated. 3. The deflection amount of the work caused by the pressing force of the tool is obtained with the tool position on the machining path where the cross-sectional area of the work changes discontinuously as the measurement point, and the data of the deflection amount of the work at each measurement point is obtained. The method for correcting a cutting error in an NC machine tool according to claim 2, wherein the amount of bending of the workpiece on the machining path at each position between the respective measurement points is interpolated and estimated.